De Luca Carlo J, Kline Joshua C, Contessa Paola
NeuroMuscular Research Center, Boston University, Boston, Massachusetts; Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts; Department of Biomedical Engineering, Boston University, Boston, Massachusetts; Department of Neurology, Boston University, Boston, Massachusetts; and Department of Physical Therapy and Athletic Training, Boston University, Boston, Massachusetts
NeuroMuscular Research Center, Boston University, Boston, Massachusetts; Department of Biomedical Engineering, Boston University, Boston, Massachusetts;
J Neurophysiol. 2014 Aug 15;112(4):962-70. doi: 10.1152/jn.00619.2013. Epub 2014 Jun 3.
Muscles are composed of groups of muscle fibers, called motor units, each innervated by a single motoneuron originating in the spinal cord. During constant or linearly varying voluntary force contractions, motor units are activated in a hierarchical order, with the earlier-recruited motor units having greater firing rates than the later-recruited ones. We found that this normal pattern of firing activation can be altered during oscillatory contractions where the force oscillates at frequencies ≥2 Hz. During these high-frequency oscillations, the activation of the lower-threshold motor units effectively decreases and that of the higher-threshold motor units effectively increases. This transposition of firing activation provides means to activate higher-threshold motor units preferentially. Our results demonstrate that the hierarchical regulation of motor unit activation can be manipulated to activate specific motoneuron populations preferentially. This finding can be exploited to develop new forms of physical therapies and exercise programs that enhance muscle performance or that target the preferential atrophy of high-threshold motor units as a result of aging or motor disorders such as stroke and amyotrophic lateral sclerosis.
肌肉由称为运动单位的肌纤维群组成，每个运动单位都由起源于脊髓的单个运动神经元支配。在持续或线性变化的随意力收缩过程中，运动单位按等级顺序被激活，较早被募集的运动单位比后来被募集的运动单位具有更高的放电频率。我们发现，在力以≥2Hz频率振荡的振荡收缩过程中，这种正常的放电激活模式会发生改变。在这些高频振荡期间，低阈值运动单位的激活有效降低，而高阈值运动单位的激活有效增加。这种放电激活的转换提供了优先激活高阈值运动单位的方法。我们的结果表明，可以操纵运动单位激活的分级调节，以优先激活特定的运动神经元群体。这一发现可用于开发新的物理治疗和运动方案，以增强肌肉性能，或针对因衰老或中风、肌萎缩侧索硬化等运动障碍导致的高阈值运动单位的优先萎缩。
